This invention relates generally to glass compositions and sealing processes and more particularly to a low temperature lead glass frit sealing composition and process.
Glass materials are used in forming seals either to bond parts of a structure together in a gas-tight manner such as, for example, in forming gas display panels or in sealing the outer surface of an article such as a recording head.
The sealing materials should have softening points which are low enough so that the temperature which is necessary to form the seal does not cause thermal damage to the parts which are being sealed or bonded. The sealing materials should also have coefficients of thermal expansion which are compatible with the surfaces being sealed.
It is known to use devitrified lead glasses for forming seals because of their relatively low softening points. It is also known to include 5% or more of TiO.sub.2 as part of the solid solution, lead glass compositions which acts to form a crystalline phase in the seal and which also lowers the coefficient of thermal expansion (CTE) so that the sealing glass will match the CTE of the surface being sealed.
Although, sealing temperatures in the order of 500.degree. to 700.degree.C are conventionally employed, some applications require sealing temperatures which are not much greater than 400.degree.C in order to avoid thermal damage to the surfaces being sealed. We have found that a glass frit composition including a lead glass and an organic vehicle will provide low temperature sealing. However, a problem occurs in that the seals may be grey-black, porous, and poorly bonded. This is believed to be caused by the reaction of residue from the organic vehicle which remains in the glass composition even at temperatures where one would expect the vehicle to have been completely removed. A glass frit sealing composition and process has now been found which permits the use of low sealing temperatures and which provides high quality seals.